1. Field of the Invention
The invention in general relates to sonar systems, and particularly, to an improved synthetic aperture multi-beam side-looking sonar system.
2. Background Information
In side-looking sonar systems, apparatus on a carrier vehicle repetitively transmits acoustic pulses (pings) to sonify a target area. Acoustic energy reflected back from the target area impinges upon a multi-element elongated receiver transducer, and beam forming circuitry creates a plurality of receiver beams such that the energy reflected from adjacent narrow strips on the target area may be portrayed as a line-by-line picture that is a pattern of highlights and shadows, analogous to an optical viewed panorama illuminated by side lighting, with objects outlined in such a way as to permit their identification.
There is considerable interest in applying the principles of synthetic aperture side looking radar to side looking sonar systems. A synthetic aperture system is based upon the generation of an effectively long antenna or receiver transducer by signal processing means rather than by the actual use of a physically long antenna or transducer. In synthetic aperture side-looking sonar systems, a multi-element receiver transducer is moved to take up sequential positions along a course line, and during movement, acoustic transmissions take place whereby the energy reflected back from the target area causes the transducer elements to provide respective output signals which are stored. After a predetermined number of sequential pings during the course of travel, all of the stored signals are suitably processed to form a plurality of synthetic aperture beams each having a higher resolution due to the longer aperture than the real aperture beam.
With the present invention, faster forward travel is possible and less processing circuitry is required as compared with conventional synthetic aperture sonar systems, and further, the arrangement allows for a synthetic aperture retrofit for various existing side-looking sonar systems.